The invention pertains to a catalyst at least comprising a hydrogenation metal component and a synthetic clay. Said catalyst is particularly suitable for hydroprocessing hydrocarbon feeds. The term xe2x80x9chydroprocessingxe2x80x9d in this context encompasses all processes in which a hydrocarbon feed is reacted with hydrogen at elevated temperature and elevated pressure. These processes include hydrodesulphurisation, hydrodenitrogenation, hydrodemetallisation, hydrode-aromatisation, hydro-isomerisation, hydrodewaxing, hydrocracking, and hydrocracking under mild pressure conditions, which is commonly referred to as mild hydrocracking.
Clays are layered silicates, also known as phyllosilicates. They are composed of a stack of elemental clay platelets. The individual clay platelets are composed of a central layer of octahedrally coordinated metal ions interlinked by means of oxygen ions. On either side of this octahedral layer there is a layer of tetrahedrally coordinated metal ions, with oxygen ions serving to link the tetrahedrally coordinated metal ions both to one another and to the octahedral layer. In addition to oxygen atoms interlinking metal ions, the clay structure contains hydroxyl groups.
To have a neutral octahedral layer, the metal ions present in that layer will have to provide a total charge of 6+ for every three octahedral cavities. This can be achieved by filling two out of every three octahedral cavities with trivalent metal ions, e.g., aluminium ions, or by filling all octahedral cavities of each set of three with divalent metal ions, e.g., magnesium ions. This gives two types of octahedral layers, viz. trioctahedral layers, which have three (divalent) cation site occupancy, and dioctahedral layers, which have two (trivalent) cation site occupancy. In dioctahedral layers one third of the octahedral sites between the oxygen atoms remains unfilled.
A neutral tetrahedral layer requires that the tetrahedral cation have a tetravalent charge. In general, the cation will be Si4+.
When lower valency cations are substituted for higher valency cations in the clay platelet structure, the clay platelet is negatively charged. This phenomenon is known as isomorphous substitution. For instance, in the octahedral layer divalent metal ions such as magnesium, zinc or nickel may be substituted for trivalent metal ions such as aluminium. The clays formed in this fashion are called montmorillonites. Alternatively, in a trioctahedral layer monovalent metal ions such as lithium may be substituted for divalent metal ions, resulting in so-called hectorites. In the tetrahedral layer trivalent metal ions, e.g., aluminium atoms, may be substituted for the silicon atoms. In the case of a clay with a trioctahedral layer, such a substitution will give a saponite, for a clay with a dioctahedral layer the result will be a beidellite.
The negative charge generated by isomorphous substitution is counterbalanced by the incorporation of hydrated cations, also known as counter-ions, into the space between the clay platelets. Generally, these cations are incorporated in the hydrated form, causing the clay to swell. For this reason clays with negatively charged clay platelets are also known as swelling clays. It is because of this negative charge that swelling clays are advantageous for use in catalysts. For, they can act as solid acids.
The use of clays in hydroprocessing catalysts is known as such, e.g., from EP-A 0 246 906. In this publication hydroprocessing catalysts are described which contain a natural clay where hydrogenation metals have been substituted for the counter-ions.
GB 1 528 982 describes a hydroprocessing catalyst containing a Group VIB metal disulphide with a hexagonal crystal structure on a layered support, e.g., a clay.
However, the known clay-containing catalysts do not always provide satisfactory results when hydrocarbon feeds are reacted with hydrogen, int. al., because insufficient clay mineral is accessible to the feed and it is not possible to fully regulate the clays"" properties.
The Catalyst According to the Invention
It has now been found that an exceptionally favourable hydroprocessing catalyst is obtained by the incorporation therein of a clay satisfying certain conditions with regard to the diameter and the degree of stacking of the clay platelets. The catalyst according to the invention at least comprises a hydrogenation metal component and a clay, with the average diameter of the clay platelets not exceeding 1 micron and the average degree of stacking of the clay platelets not exceeding 20 sheets per stack. The two parameters are easily determined by means of transmission electron microscopy. Furthermore, the clay platelets have to be negatively charged. Neutral clay platelets, i.e., clay platelets which have not been subject to isomorphous substitution, are catalytically inactive.
Because there are restrictions to the diameter and the degree of stacking of the clay platelets, their surface area is readily accessible to the feed, giving a very active catalyst.
The average diameter of the clay platelets is not more than 1 micron, and is preferably between 1 nm and 0.5 micron, more preferably in the range of 1 nm to 0.1 micron, most preferably in the range of 1 to 50 nm. The average degree of stacking of the clay platelets is not more than 20 platelets per stack, preferably not more than 10 platelets per stack, more preferably not more than 5 platelets per stack, and most preferably not more than 3 platelets per stack. The lower limit, needless to say, is constituted by unstacked clay platelets, which have a xe2x80x9cdegree of stackingxe2x80x9d of 1. As regards isomorphous substitution, at least 0.1 atomic %, as compared with the neutral clay mineral of the cations, can be replaced by cations of a lower valency. Preferably, at least 1 atomic %, more preferably at least 5 atomic %, of the cations in the clay platelets is replaced by cations of a lower valency. In the octahedral layer, preferably not more than 50 atomic % of the metal ions is replaced by ions of a lower valency as compared with the neutral situation, more preferably not more than 30 atomic % is replaced. In the case of the tetrahedral layer, preferably not more than 30 atomic % of the tetravalent metal ions present is replaced by metal ions of a lower valency, more preferably not more than 15 atomic %. Isomorphous substitution may occur only in the octahedral layer, only in the tetrahedral layer, or in both layers. In this context the term isomorphous substitution also refers to the removal of cations without the incorporation into the lattice of replacement cations, by which vacancies are produced. It will be clear that this removal also generates negative charges.
The trivalent ions in the octahedral layer preferably are aluminium, chromium, cobalt (III), iron (III), manganese (III), titanium (III), gallium, vanadium, molybdenum, tungsten, indium, rhodium, and/or scandium. The divalent ions in the octahedral layer preferably are magnesium, zinc, nickel, cobalt (II), iron (II), manganese (II), copper (II) and/or beryllium, and the monovalent ions preferably are lithium ions.
The tetravalent ions in the tetrahedral layer preferably are silicon, titanium (IV), and/or germanium, for which may be substituted trivalent ions preferably selected from aluminium, borium, gallium, chromium, iron (III), cobalt (III), and/or manganese (III). A portion of the hydroxyl groups present in the clay platelets may be replaced by fluorine if so desired.
Clays suitable for use in the catalyst according to the invention include clays with a composition as given in the following table:
As was stated earlier, it is of vital importance to the catalyst according to the invention that the clay platelets be negatively charged. This can be effected simply by ensuring that metal ions of a lower valency than is required for the neutral state are incorporated into the octahedral layer or the tetrahedral layer or both. In the catalyst according to the invention use can be made of clays which have had isomorphous substitution in the octahedral layer as well as clays which have had isomorphous substitution in the tetrahedral layer. Since the negative charge is closer to the surface of the clay platelets in the case of substitution in the tetrahedral layer, substitution in the tetrahedral layer will generally give more strongly acid sites than substitution in the octahedral layer. Isomorphous substitution in the tetrahedral layer gives a structure of acid sites which somewhat resembles the acid sites structure found in zeolites.
Optionally, the counter-ions in the interlayer between the clay platelets can be replaced by H3O+ ions. Generally, such a substitution does not involve suspending the clay in a concentrated acid, for the acid may react with the cations in the clay structure, resulting in the cations being lixiviated and ending up in the interlayer. If it is desired to introduce H3O+ ions into the interlayer between clay platelets, the first step is to use ion exchange to incorporate hydrolysing metal ions into the interlayer. Hydrolysis will then give hydrogen ions. These Brxc3x8nsted acid sites can be converted into Lewis acid sites by heating. Alternatively, Brxc3x8nsted sites can be achieved by substituting ammonium ions for cations and then heating the whole. This process will result first of all in ammonia desorption, leaving a proton to form a Brxc3x8nsted site. Heating to a higher temperature results in water desorption, forming a Lewis site. Such Lewis sites are of particular interest for catalytic purposes.
Swelling clays suitable for use in the catalyst according to the invention are disclosed, int. al., in Netherlands patent application No. 9401433.
In this patent application clays are described which have clay platelets satisfying the requirements as to degree of stacking and size of the platelets, thus rendering them suitable for use in the catalyst according to the invention. This patent application further describes clay minerals composed of clay platelets of the desired degree of stacking and sheet size where the clay platelets are not so much stacked as placed one on top of the other at an angle in a xe2x80x9chouse of cardsxe2x80x9d structure. The advantage of this house of cards structure is that it gives comparatively wide pores of a diameter of the order of 6 nm and higher. The greater part of the specific surface area of such a clay is in pores having a diameter of 6 nm or higher. A feature of such a structure is that its X-ray diffraction pattern has no or hardly any (001) reflections, indicating that there is hardly any stacking.
The aforesaid patent application also describes a process for the preparation of clays suitable for use in the catalyst according to the present invention, which process has the advantage over the conventional processes of forming clays having the desired properties in regard of the size and the degree of stacking of the clay platelets. In addition, compared with the known processes the implementation and scaling up of said process are particularly simple.
In the broadest form, the implementation of the process described in said patent application is as follows. An aqueous mixture of the components needed to achieve synthesis, viz. oxides of the tetravalent ions to be incorporated into the tetrahedral layer and the ions to be incorporated into the octahedral layer, is brought to a pH in the range of 3 to 9. The whole is then aged for some time, e.g., for 0,5 to 50 hours, at a temperature in the range of 600 to 350xc2x0 C., the pH being kept at the desired value. In this process a solid product is formed, which is isolated, for instance by filtration, and, if so desired, washed and/or subjected to an ion exchange prior to being dried. The process preferably is carried out in the absence of chloride.
One possible way of implementing the process is by mixing the starting products prior to the preparation and then rapidly bringing the whole to the pH at which the clay is to be formed. During the subsequent heating the pH is kept at this value, with stirring, by the addition of a base. This may take the form of a base being injected below the surface of the liquid, or of adding a compound which will decompose to form a base.
It is preferred, however, to prepare a suspension containing solid silica and metal ions to be incorporated into the octahedral layer, and to slowly increase the pH of this slurry by the addition of a base or the partial decomposition of a base precursor. For example, a silica gel is prepared, the pH of which is reduced to a value at which the metal ions to be incorporated into the octahedral layer are still soluble. Next, the metal ions to be incorporated into the octahedral layer are added. Excess urea is added, and the whole is aged with stirring. Base is released by the decomposition of the urea, resulting in a slow increase in the pH of the suspension to form a clay mineral. The nature of the obtained clay can be altered by varying the nature of the metal ions added. For instance, adding a mixture of magnesium ions and zinc ions will give a clay of which the octahedral layer contains both magnesium ions and zinc ions.
The size of the clay platelets is dependent on the aging temperature and the aging period. The higher the aging temperature is and the longer the aging period, the larger the clay platelets will be. The size is also dependent on the nature of the metal ions to be incorporated into the octahedral layer. If, say, zinc ions are used, the platelets obtained will be much larger than when magnesium ions are used.
The degree of stacking is dependent on the ionic strength of the solution. A high ionic strength will give much-stacked structures, while a low ionic strength will lead to structures exhibiting little stacking.
A simple way of preparing a clay in which aluminium is substituted for silicon in the octahedral layer is by treating silica with a basic aluminate solution, acidifying the whole to a pH at which the metal ions to be incorporated into the octahedral layer are still soluble, adding these metal ions, and then homogeneously increasing the pH of the solution. Preference is given in this process to a gel prepared by adding a basic aluminate to a silica gel. Following acidification the metal ions to be incorporated into the octahedral layer and an overmeasure of a compound which decomposes to form a base, e.g., urea, are added to homogeneously increase the pH. Next, the whole is aged with stirring, in which process the insoluble clay mineral is formed. This process produces clay minerals which satisfy the average platelet diameter and degree of stacking requirements set for use of the clay in the catalyst according to the invention. The ratio of silicon atoms to aluminium atoms in the tetrahedral layer, and hence part of the acidity of the clay, can be regulated through the ratio of silicon ions to aluminium ions in the gel. The gel""s silicon atoms and aluminium atoms by and large end up in the tetrahedral layer of the formed clay.
If so desired, the clays may be pillared. This involves providing oligomers or polymers of, say, aluminium, chromium, zirconium or titanium hydrated by ion exchange between the clay platelets. One example of a known compound used to provide pillars is the aluminium-13 cluster, a complex of 13 aluminium ions interlinked by hydroxyl groups and oxygen atoms. The incorporation of pillars between the clay platelets ensures that the space between the clay platelets is kept open during drying, thus increasing the accessible surface area. Processes for providing pillars between clay platelets include those described in U.S. Pat. Nos. 4,952,544, 4,637,991, and 4,766,099. The invention further pertains to a catalyst containing a hydrogenation metal component and a pillared clay.
In Netherlands patent application No. 9401433 a process for producing pillars is described where the pH of a solution of the metal ions which are to form the pillars is slowly increased, e.g., using urea. This process makes it possible to produce larger pillars than those known so far. This is done, for instance, by preparing an aluminium solution having a low pH, which pH is then increased in a controlled manner. This first results in the forming of aluminium-13 complexes. If the pH is increased still further, aluminium will precipitate on the aluminium-13 complexes, resulting in larger aluminium complexes. These can be incorporated between the clay platelets by means of ion exchange. Catalysts containing a hydrogenation metal component and pillared clay minerals as described in the aforementioned patent application are also part of the present invention. Apart from that, it should be noted that because the clay minerals used in the catalyst according to the invention have such small clay platelets and a low degree of stacking, rendering the surface area of the clay platelets readily accessible, it is not necessary by any means to always pillar the clay.
Netherlands patent application No. 9401433 also discloses the use of activated carbon, e.g., in the form of carbon filaments, as support material for the clay. This embodiment is of interest to hydroprocessing applications, and the present invention encompasses a hydroprocessing catalyst containing a hydrogenation metal component and a clay on a support of activated carbon as one of its embodiments.
The clays used in the catalyst according to the present invention generally have a specific surface area in the range of 100 to 1000 m2/g, depending on the nature of the metals present in the octahedral layer. The pore volume, determined by means of nitrogen sorption, is in the range of 0.03 to 1.5 ml/g, again depending on the nature of the metals present in the octahedral layer. In general, the catalyst according to the invention contains 1 to 99 wt.% of clay.
The catalyst according to the invention at least comprises a hydrogenation metal component. As will be evident to the skilled person, the word xe2x80x9ccomponentxe2x80x9d in this context denotes the metallic form of the metal, its oxide form, or its sulphide form, or any intermediate, depending on the situation. The hydrogenation metals are selected from the Periodic Table""s Group VIB and Group VIII metals. The nature of the hydrogenation metal present in the catalyst is dependent on the catalyst""s envisaged application. If, say, the catalyst is to be used for hydrogenating aromatics in hydrocarbon feeds, the hydrogenation metal used preferably will be one or more noble metals of Group VIII, preferably platinum, palladium, or a mixture thereof. In this case the Group VIII noble metal preferably is present in an amount of 0.05-5 wt. %, more preferably in an amount of 0.1 to 2 wt. %, calculated as metal. If the catalyst is to be used for removing sulphur and/or nitrogen, it will generally contain a Group VIB metal component combined with a Group VIII metal component. In that case, preference can be given to the combination of molybdenum, tungsten, or a mixture thereof and nickel, cobalt, or a mixture thereof. The Group VIB hydrogenation metal preferably is present in an amount of 2 to 40 wt. %, more preferably in an amount of 5 to 30 wt. %, most preferably in an amount of 5 to 25 wt. %, calculated as trioxide. The Group VIII non-noble hydrogenation metal preferably is present in an amount of 1 to 10 wt. %, more preferably in an amount of 2-8 wt. %, calculated as oxide. If the catalyst is to be used in hydrocracking or mild hydrocracking, use will be made of either a Group VIII noble metal or a combination of a Group VIB metal and a Group VIII metal.
Clays possess a remarkable property as compared with well-known acidic components such as silica-alumina and zeolites in that they enable the hydrogenation metals as described above to be incorporated into the clay platelet structure. For instance, cobalt or nickel may be present in the octahedral layer. In order to be catalytically active, these metals must be removed from the clay platelet structure during catalyst use. This can be done, e.g., by means of reduction or sulphidation, for instance when the catalyst is sulphided under reducing conditions prior to use. Alternatively, the hydrogenation metals can be incorporated into the interlayer between the clay platelets through ion exchange.
In addition to the clay satisfying the aforementioned conditions with regard to clay platelet size and maximum number of clay platelets in a stack, the catalyst may comprise matrix materials, e.g., alumina, silica, silica-alumina, silica-magnesia, zirconia, titania, silica-zirconia, silica-titania, other clays, molecular sieves, aluminophosphates, and mixtures of these materials. These matrix materials can function as binder for the clay platelets, thus improving the attrition resistance of the catalyst particles. They can also function as filler material, acting as diluent of the cracking activity of the clay platelets, thus making it possible to regulate the cracking activity of the catalyst. On the other hand, these matrix materials can also add a catalytic activity of their own to the catalyst according to the invention. For example, the incorporation of silica-alumina or a molecular sieve component into the catalyst composition will add a specific cracking activity to the catalyst composition.
The amount of matrix material which is present in the catalyst composition according to the invention will depend on its function. Preferably, the catalyst according to the invention contains at least 5 wt. % of matrix material, calculated on the weight of the catalyst composition. Binder/filler matrix materials are generally present in an amount of 0-90 wt. %, calculated on the weight of the catalyst composition. For example, catalysts are envisaged containing 10-50 wt. % of clay component, 1-45 wt. % of hydrogenation metal component, and the balance, that is, 89-50 wt. %, of binder/filler. Suitable binder/filler matrix materials are, for example, alumina, silica, titania, and zirconia, with alumina generally being especially suitable. The amount of matrix materials with catalytic cracking activity will depend upon the activity desired. If these types of catalytically active matrix materials are present, they are preferably present in an amount of 10-80 wt. %, calculated on the weight of the catalyst composition, more preferably in an amount of 20-50 wt. %. Of course catalysts comprising two types of matrix material are also envisaged in the present invention.
Optionally, the catalyst can further contain other components such as phosphorus. It will be obvious to the skilled person that phosphorus can be incorporated into the catalyst in a suitable manner by contacting the catalyst during any one of its formative stages with an appropriate quantity of a phosphorus-containing compound, e.g., phosphoric acid. For instance, the catalyst can be impregnated with an impregnating solution comprising phosphorus in addition to any other components. If the catalyst according to the invention contains phosphorus, this compound is preferably present in an amount of 0.5-10 wt. %, calculated as P2O5, based on the weight of the catalyst composition.
The catalyst according to the invention generally has a specific surface area in the range of 50 to 600 m2/g, preferably in the range of 100 to 400 m2/g, and a pore volume in the range of 0.1 to 1.5 ml/g, preferably in the range of 0.3 to 1.2 ml/g.
Preparation of the Catalyst According to the Invention
The catalyst according to the invention can be prepared in several ways.
For instance, it is possible to extrude the clay into particles, calcine the extrudates, and impregnate the calcined extrudates with an impregnating solution containing salts of the hydrogenation metals to be introduced, optionally in combination with other components such as phosphoric acid and/or complexing agents known in the art. Alternatively, the clay can be mixed with other support materials which, as explained above, may have their own catalytic activity, whereupon this mixture can be extruded and the resulting extrudates calcined. The calcined extrudates can then be impregnated as described above. It is also possible to add certain hydrogenation metal components to the catalyst composition prior to extrusion, more particularly, it is proposed to mix the clay and any other support materials with molybdenum oxide, after which the resulting mixture is extruded and calcined.
As was stated earlier, clays containing hydrogenation metals of their own can also be used in the catalyst according to the invention. The hydrogenation metals can be added, e.g., during the preparation of the clay, resulting in their incorporation into the octahedral layer. While it may be that the catalyst contains only those hydrogenation metals introduced via the clay, it is also possible to incorporate other, additional hydrogenation metals into the catalyst composition. Furthermore, the hydrogenation metals can be incorporated as counter-ions between the clay platelets, to counterbalance the clay platelets"" negative charge.
It will be evident to the skilled person that it is also possible to combine the different aspects of the processes described above. Thus, a portion of the hydrogenation metals can be introduced via impregnation, while another portion is mixed with the clay before it is formed into a support, or a portion of the hydrogenation metals is incorporated into the catalyst composition by way of the clay component, while another portion is added to the catalyst composition by impregnation of the shaped support.
The catalyst particles may have many different shapes. The suitable shapes include spheres, cylinders, rings, and symmetric or asymmetric polylobes, for instance tri- and quadrulobes. The particles usually have a diameter in the range of 0.5 to 10 mm, and their length likewise is in the range of 0.5 to 10 mm.
If the catalyst contains non-noble Group VIII metals and/or Group VIB metals as hydrogenation metals, it is preferably sulphided prior to use. This involves converting the metal components in the catalyst to their sulphided form. The sulphiding can be done by means of processes known to the skilled person, e.g., by contacting the catalyst in the reactor at rising temperature with hydrogen and a sulphurous feed, or with a mixture of hydrogen and hydrogen sulphide. If the catalyst is a Group VIII noble metal, there is no need for sulphiding as a rule, and a reducing step, e.g., with hydrogen, will suffice.
As stated before, if the clay component contains hydrogenation metals such as cobalt or nickel, these will be freed from the clay by sulphidation. Because the hydrogenation metals are distibuted homogeneously through the clay, the hydrogenation metals will be distributed homogeneously over the catalyst composition after sulphidation.
Use of the Catalyst According to the Invention
Depending on their composition, the catalysts according to the invention can be used in virtually all hydroprocessing processes to treat a plurality of feeds under wide-ranging reaction conditions, e.g., at temperatures in the range of 200xc2x0 to 440xc2x0 C., hydrogen pressures in the range of 5 to 300 bar, and space velocities (LHSV) in the range of 0.05 to 10 hxe2x88x921.
For example, certain catalysts according to the invention are suitable for use in the hydrocracking of heavy feedstocks to form middle distillates. For these hydrocracking processes, the following values for the relevant process parameters apply:
temperature: in the range of 2300 to 450xc2x0 C.;
hydrogen pressure: in the range of 100 to 250 bar;
space velocity: in the range of 0.2 to 3 hoursxe2x88x921;
H2/oil ratio: in the range of 300 to 2000 Nl/l.
Generally, the conditions selected are such as will give a conversion of at least 70 wt. %. The term conversion in this context refers to the weight, in per cent, of obtained product with a boiling point below 391xc2x0 C. (where applicable, this weight is corrected by taking into account the weight of the portion of the feedstock which already boils below 391xc2x0 C.) vis-xc3xa1-vis the weight of the feedstock deployed. An example of a catalyst according to the invention which is suitable for use in hydrocracking to produce middle distillates is a catalyst comprising 3-40 wt. % of hydrogenation metals, preferably comprised of a combination of Ni and Mo or W, 1-60 wt. % of clay component, preferably 10-50 wt. %, 3-55 wt. % of zeolite, preferably 10-50 wt. %, and the balance alumina.
An example of a catalyst according to the invention which is suitable for the production of diesel by way of hydrocracking comprises a Group VIB hydrogenation metal component, a non-noble Group VIII hydrogenation metal component, and two crystalline acid components, namely a clay component with the required properties as to platelet size and stacking degree in combination with a Y-zeolite with a unit cell size in the range of 2.400-2.480 nm. The clay component is for example a magnesium saponite.
The use of the catalysts according to the invention in mild hydrocracking processes is also envisaged. For mild hydrocracking processes, the following values hold for the relevant process parameters:
temperature: in the range of 350xc2x0 to 450xc2x0 C.;
hydrogen pressure: in the range of 25 to 100 bar, preferably in the range of 40 to 80 bar;
space velocity: in the range of 0,2 to 3 hoursxe2x88x921;
H2/oil ratio: in the range of 200 to 1000 Nl/l.
Generally, the conditions selected are such as will give a conversion of at least 20 wt. %. The definition of conversion is the same as that given above.
An example of a catalyst according to the invention which is suitable for use in mild hydrocracking to produce middle distillates is a catalyst comprising 3-40 wt. %, preferably 10-40 wt. %, of hydrogenation metal components, which preferably are a combination of Ni and Mo or W, 5-75 w t.% of a clay component, preferably 15-50 wt. %, and 0-95 wt. %, preferably 5-50 wt. %, of alumina binder.
The catalysts according to the present invention a re also very suitable for use in hydroisomerisation, more particularly for the difunctional hydroisomerisation of long chain paraffins. These long chain paraffins, also known as waxes, are molecules that have a negative effect on the quality of diesel fuels and lube oils. In diesel fuels, the wax molecules tend to crystallise at unacceptably high temperatures, so rendering the diesel unsuitable for fuel applications during wintertime. In lube oils, waxes will mainly affect the viscosity. Hence, these molecules must be removed. Two ways to achieve this are known in the literature, namely cracking the molecules to lower boiling molecules and isomerisation of the molecules to isoparaffins. A (hydro)cracking dewaxing catalyst will by nature convert some of the feedstock, namely the n-paraffins, to products outside the desired boiling range, thus limiting the attainable yields of middle distillate. A hydroisomerisation process, on the other hand, will convert the n-paraffins to isoparaffins, which have boiling points in the desired range but melting/crystallisation points (i.e., cloud points) much lower than those of the n-paraffins. It has been found that the catalyst according to the invention is also suitable for use in the hydroisomerisation of wax-containing feedstocks. Such a catalyst contains a hydrogenation component consisting of one or more of Group VIB metal components and Group VIII metal components, more particularly, the Group VIII noble metals. Most preferably, the hydrogenation component is platinum, palladium, or a combination of the two. The presence of the clay component in the catalyst according to the invention is advantageous for the hydroisomerisation of wax-containing feedstocks, because it has a combination of desirable properties. The low acidity of the clay precludes hydrocracking of the product isoparaffins. The properties of the clay are such that a good dispersion of the hydrogenation component is ensured. The effects of mass diffusion limitation are eliminated by controlling the properties of the support. It is preferred in this specific application to prevent hydrocracking through binder-support interactions by using a binder material which does not give rise to such interactions, e.g., silica or titania.
Alternatively, it may be preferable to shape the synthetic acid saponite support without any binder whatsoever. A particularly preferred catalyst for use in hydroisomerisation is a catalyst comprising 0.1-2.0 wt. % of platinum, palladium, or a mixture thereof, 1-99.9 w t.%, preferably 10-50 wt. %, of clay component, and 0-98.9 wt. %, preferably 50-90 wt. %, of silica, titania, or a mixture thereof.